End-effectors attached to devices such as robotic arms are well known. These end-effectors often have operational members that perform operations on items. One common type of operational members are pick-up members which can be used to pick up, move and release items.
The use of devices as such as robotic arms with end effectors, that can perform operations on items, is also well known in various industries, such as for example, in the packaging industry. Such robotic arms use a variety of end effectors, for example, to move items from an article feed conveyor into open receptacles such as for example, cardboard boxes. Advantageously, robotic arms and their end-effectors can be moved through a wide range of orientations and positions in a three-dimensional space. One example of the use of a robotic arm and end effector to package items is disclosed in U.S. Pat. No. 5,060,455 (“Robotic Case Packaging System and Method”), the contents of which are hereby incorporated by reference.
Robotic arms are traditionally constructed as a cascade of several joined sections, each of which can be rotated and translated in a three-dimensional space so as to achieve a desired position of the end section of the robotic arm, and thus achieve a desired position and orientation in the three-dimensional space for the end effector attached to the end section of the robotic arm. Disadvantageously, because several different sections of traditional robotic arms have to be separately controlled, such robotic arms are very slow, and therefore not particularly well suited for use with high rate packaging systems. However, a more recent robotic arm that can move at very high speeds is the robotic arm disclosed in U.S. Pat. No. 4,976,582 (“Device for the Movement and Positioning of an Element in Space”), the contents of which are hereby incorporated by reference. This robotic arm, sometimes referred to as a “Delta” robot or a “Spider” robot uses three independent and non-joined control arms extending from a base element and attached to a movable element to position and orient the movable element in three-dimensional space. An end effector is attached to the movable element. Preferably, the end effector can be rotated about its center by connecting a rotatable shaft that is connected to a motor preferably positioned at the base element of the Delta robot. Advantageously, this design allows the movable element to be moved at accelerations ranging between 12 G to 50 G.
Because of the high speeds at which Delta robots can move, Delta robots have been used in industry to package items. For example, a packaging system manufactured by SIG Demaurex uses a Delta robot to package various food items. This packaging system uses an end effector comprising of six pick-up members to simultaneously pick-up six items. Gripping of the items in the packaging system is usually achieved by suction cups on the end effector which grip one or more items. The suction is applied to the cups through the use of a vacuum system. Once the end effector attached to the movable element in the Delta robot has picked up the items, the end effector is moved to a position proximate a receptacle at some desired position relative to the rest of the packaging system. At this release position the items can be deposited into the receptacle.
Advantageously, the positions of the pick-up members on the end effector can be adjusted so that the pick-up members can pick-up several items at the same time, that are far apart from each other. Subsequently the items held by the end-effector can be converged, by moving the pick-up members toward each other, thus bringing the items closer to each other. Having adjusted the spacing of the items, they can be deposited into a single receptacle in a more closely packed configuration.
Known designs of end effectors for simultaneous transport of a number of items use pneumatic rods, or equivalent actuation mechanism, that are attached to each one of the pick-up members on the end effector to control the positions of those pick-up members on the end effector. One of the main problems with such end effector designs is the high complexity involved in individually controlling the position of the pick-up members. Additionally, the physical size of each actuation device places constraints on the maximum number of actuation devices that can be combined to form the actuation mechanism of an end effector.
Another problem with the use of Delta robots to package items is the limitation of the load weight that can be carried by the end effector due to the high speeds at which the movable element, and the end effector attached to it, move. A heavy weight load would necessarily reduce the maximum acceleration that can be obtained for the movable element and the end effector. Thus, one of the important considerations in the design and use of an end effector is the weight of the end effector. The lower the weight of the end effector, the more weight that can then be picked-up by the end effector for transport to a receptacle. With current designs of end effectors for simultaneous transport of multiple items, the use of separate pneumatic rods to control individual pick-up member adds considerable weight to the overall weight of the end effector. This reduces the total weight that can be picked-up by the end effector for transporting an article to a receptacle.
It would therefore be desirable to have a lighter weight end effector, that uses a less complex and cumbersome actuation mechanism to control the positions of the pick-up members on the end effector.
It is also desirable to be able have an end effector which can perform a first operation on a group of several items spaced at a first pitch and then group those items into at least two groups, each item in the two groups being at a second pitch, and perform a second operation on the items in both groups at the same time.